An example of an apparatus for molding a stretched film made of resin is shown in FIGS. 4 and 5. FIG. 4 shows an example of an apparatus for producing a biaxially oriented film made of resin. FIG. 5 shows a guide rail of a transversely stretching device of FIG. 4. As shown in FIGS. 4 and 5, the apparatus for producing a biaxially oriented film has an extruder 9 for fusing and kneading resin, a die head (T die) 10 for shaping the fused and kneaded resin into a raw sheet and extruding the resin, a longitudinally stretching device 11 for longitudinally stretching the raw sheet, a transversely stretching device 13 for widthwise stretching the sheet which has been longitudinally stretched, and a drawing/winding device 14 for drawing and winding a biaxially oriented film stretched longitudinally and transversely. The transversely stretching device 13 has a pair of guide rails 12 which circulate, a plurality of tenter clips 15 which circulate on the guide rails 12 at regular intervals, and a device for heating the sheet.
As shown in FIG. 5, in the transversely stretching device 13, the longitudinally stretched sheet is widthwise stretched along large-width portions 12a, 12b of the guide rails 12 with both edges of the sheet being successively gripped by the plurality of tenter clips 15, while the sheet is being heat-treated to form a biaxially oriented film stretched longitudinally and transversely. As shown in FIG. 4, the biaxially oriented film is wound by the drawing/winding device 14.
A rolling bearing for the tenter clip 15 is exposed to a temperature of 200 to 250° C. inside the transversely stretching device 13 for heat-treating the sheet. Therefore as a lubricant for the rolling bearing for the tenter clip, generally fluorine grease is enclosed therein in consideration of heat resistance thereof.
Ester oil is often used to lubricate the guide rail 12. When the ester oil penetrates into the bearing in which the fluorine grease is enclosed, the fluorine grease leaks from the bearing because the ester oil has a higher degree of affinity for metal than the fluorine grease. As a result, the heat resistance of the bearing deteriorates. In the rolling bearing for use in the tenter clip, as a method for preventing the leak of the fluorine grease, a method of using a mixed oil of the ester oil and fluorine oil as a base oil is known (see patent document 1).
The method of using the mixed oil of the ester oil and the fluorine oil as the base oil is effective for preventing the leak of the fluorine grease. By using an appropriate material for a sealing apparatus of the bearing, for example, a sealing member of the bearing, it is possible to effectively prevent the penetration of the ester oil and the leak of the fluorine grease. In this case, as the sealing apparatus, a noncontact or light contact sealing member made of rubber is suitable. In consideration of an atmospheric temperature, generally fluororubber is used as the rubber material. As a fluororubber composition which is conventionally used as a material for sealing the bearing, generally vinylidene fluoride rubber (hereinafter referred to as FKM) such as a vinylidene fluoride-hexafluoropropylene binary copolymer (VDF-HFP), a ternary copolymer (VDF-HFP-TFE) obtained by adding tetrafluoroethylene to the above-described binary copolymer, and the like are used.
However, the above-described fluororubber compositions may swell depending on a state of contact with oil and a temperature because the fluororubber compositions have a high polarity and a high affinity for the ester oil. Generally the sealing member is made of a composite material consisting of a core made of a metal plate and rubber. When the rubber portion swells, a sealing portion of the noncontact sealing member contacts oil or in the case of the light contact sealing member, the tensional force of the sealing portion increases. As a result, there arises a problem that the rotational torque of the bearing increases.
Because the film-stretching apparatus is used at high temperatures, generally an antioxidant such as an amine compound is added to the ester oil serving as the lubricating oil for the guide rail to prevent oxidative deterioration thereof. When amine contacts the FKM, a crosslinking reaction occurs at the vinylidene fluoride of the FKM and consequently the rubber hardens and deteriorates.
Patent document 1: Japanese Patent Application Laid-Open No. 2004-301167